Classify the following bonds as ionic, polar covalent, or covalent, and give your reasons:
(a) the CC bond in H3CCH3,
(b) the KI bond in KI,
(c) the NB bond in H3NBCl3,
(d) the CF bond in CF4.
The Correct Answer and Explanation is:
To classify the bonds in the given compounds as ionic, polar covalent, or covalent, we can analyze the electronegativity differences between the atoms involved and the nature of the bonds.
(a) The C-C bond in H₃C-CH₃ (Ethane)
Classification: Covalent
Reasoning: The C-C bond in ethane is a nonpolar covalent bond. Both carbon atoms have the same electronegativity (approximately 2.5 on the Pauling scale). Since the electronegativity difference between the two carbon atoms is zero, the electrons are shared equally, resulting in a nonpolar covalent bond.
(b) The K-I bond in KI (Potassium Iodide)
Classification: Ionic
Reasoning: The bond between potassium (K) and iodine (I) in KI is classified as ionic. Potassium is a metal with a low electronegativity (about 0.8), and iodine is a nonmetal with a higher electronegativity (approximately 2.5). The large electronegativity difference (about 1.7) results in the complete transfer of an electron from potassium to iodine, leading to the formation of K⁺ and I⁻ ions. This transfer of electrons and subsequent electrostatic attraction between the oppositely charged ions is characteristic of ionic bonds.
(c) The N-B bond in H₃NBCl₃ (Borane Amine)
Classification: Polar Covalent
Reasoning: The bond between nitrogen (N) and boron (B) in H₃NBCl₃ is polar covalent. Nitrogen has an electronegativity of about 3.0, while boron has an electronegativity of approximately 2.0. The electronegativity difference of about 1.0 indicates that the electrons in the N-B bond are not shared equally, with nitrogen pulling the bonding electrons closer to itself, thus creating a dipole moment.
(d) The C-F bond in CF₄ (Carbon Tetrafluoride)
Classification: Polar Covalent
Reasoning: The bond between carbon (C) and fluorine (F) in CF₄ is polar covalent. Carbon has an electronegativity of around 2.5, while fluorine has the highest electronegativity at about 4.0. The difference of approximately 1.5 means that fluorine attracts the shared electrons more strongly than carbon, resulting in a polar bond with a partial negative charge on fluorine and a partial positive charge on carbon.
Summary:
- C-C in H₃C-CH₃: Covalent (nonpolar)
- K-I in KI: Ionic
- N-B in H₃NBCl₃: Polar Covalent
- C-F in CF₄: Polar Covalent
This classification highlights how differences in electronegativity influence bond character, contributing to the physical properties of the compounds involved.